Galaxy HiCExplorer 3: a web server for reproducible Hi-C, capture Hi-C and single-cell Hi-C data analysis, quality control and visualization

Chromatin-site-specific accessibility: A microtopography-regulated door into the stem cell fate

Biomaterials that mimic extracellular matrix topography are crucial in tissue engineering. Previous research indicates that certain biomimetic topography can guide stem cells toward multiple specific lineages. However, the mechanisms by which topographic cues direct stem cell differentiation remain unclear. Here, we demonstrate that microtopography influences nuclear tension in mesenchymal stem cells (MSCs), shaping chromatin accessibility and determining lineage commitment. On aligned substrates, MSCs exhibit high cytoskeletal tension along the fiber direction, creating anisotropic nuclear stress that opens chromatin sites for neurogenic, myogenic, and tenogenic genes via transcription factors like Nuclear receptor TLX (TLX). In contrast, random substrates induce isotropic nuclear stress, promoting chromatin accessibility for osteogenic and chondrogenic genes through Runt-related transcription factors (RUNX). Our findings reveal that aligned and random microtopographies direct site-specific chromatin stretch and lineage-specific gene expression, priming MSCs for distinct lineages. This study introduces a novel framework for understanding how topographic cues govern cell fate in tissue repair and regeneration.

Inter-chromosomal transcription hubs shape the 3D genome architecture of African trypanosomes

The eukaryotic nucleus exhibits a highly organized 3D genome architecture, with RNA transcription and processing confined to specific nuclear structures. While intra-chromosomal interactions, such as promoter-enhancer dynamics, are well-studied, the role of inter-chromosomal interactions remains poorly understood. Investigating these interactions in mammalian cells is challenging due to large genome sizes and the need for deep sequencing. Additionally, transcription-dependent 3D topologies in mixed cell populations further complicate analyses. To address these challenges, we used high-resolution DNA-DNA contact mapping (Micro-C) in Trypanosoma brucei, a parasite with continuous RNA polymerase II (RNAPII) transcription and polycistronic transcription units (PTUs). With approximately 300 transcription start sites (TSSs), this genome organization simplifies data interpretation. To minimize scaffolding artifacts, we also generated a highly contiguous phased genome assembly using ultra-long sequencing reads. Our Micro-C analysis revealed an intricate 3D genome organization. While the T. brucei genome displays features resembling chromosome territories, its chromosomes are arranged around polymerase-specific transcription hubs. RNAPI-transcribed genes cluster, as expected from their localization to the nucleolus. However, we also found that RNAPII TSSs form distinct inter-chromosomal transcription hubs with other RNAPII TSSs. These findings highlight the evolutionary significance of inter-chromosomal transcription hubs and provide new insights into genome organization in T. brucei.

Remodeling of Il4-Il13-Il5 locus underlies selective gene expression

The type 2 cytokines, interleukin (IL)-4, IL-13 and IL-5 reside within a multigene cluster. Both innate (ILC2) and adaptive T helper 2 (TH2) lymphocytes secrete type 2 cytokines with diverse production spectra. Using transcription factor footprint and chromatin accessibility, we systemically cataloged regulatory elements (REs) denoted as SHS-I/II, KHS-I/II, +6.5kbIl13, 5HS-I(a, b, c, d, e), 5HS-II and 5HS-III(a, b, c) across the extended Il4-Il13-Il5 locus in mice. Physical proximities among REs were coordinately remodeled in three-dimensional space after cell activation, leading to divergent compartmentalization of Il4, Il13 and Il5 with varied combinations of REs. Deletions of REs revealed no single RE solely accounted for selective regulation of a given cytokine in vivo. Instead, individual RE differentially contribute to proper genomic positioning of REs and target genes. RE deletions resulted in context-dependent dysregulation of cytokine expression and immune response in tissue. Thus, signal-dependent remodeling of three-dimensional configuration underlies divergent cytokine outputs from the type 2 loci.

Chromosome-level genome assembly of the medicinal insect Blaps rhynchopetera using Nanopore and Hi-C technologies

Blaps rhynchopetera Fairmaire is a significant medicinal resource in southwestern China. We utilized Nanopore and Hi-C technologies in combination to generate a high-quality, chromosome-level assembly of the B. rhynchopetera genome and described its genetic features. Genome surveys revealed that B. rhynchopetera is a highly heterozygous species. The assembled genome was 379.24 Mb in size, of which 96.03% was assigned to 20 pseudochromosomes. A total of 212.93 Mb of repeat sequences were annotated, and 26,824 protein-coding genes and 837 noncoding RNAs were identified. Phylogenetic analysis indicated the divergence of the ancestors of B. rhynchopetera and its closely related species Tenebrio molitor at about 85.6 million years ago. The colinearity analysis showed that some chromosomes of B. rhynchopetera may have had fission events, and it has a good synteny relationship with Tribolium castaneum. Furthermore, in the enrichment analyses, the gene families related to detoxification and immunity of B. rhynchopetera facilitated the understanding of its environmental adaptations, which will serve as a valuable research resource for pest control strategies and conservation efforts of beneficial insects. This high-quality reference genome will also contribute to the conservation of insect species diversity and genetic resources.

ppHiC: Interactive exploration of Hi-C results on the ProteinPaint web portal

The ProteinPaint Hi-C tool (ppHiC) facilitates web-based visualization and collaborative exploration of Hi-C data, a vital resource for understanding three-dimensional genomic structures. ppHiC allows researchers to easily analyze large Hi-C datasets on a web browser without requiring the computational expertise that has heretofore limited access to this complex genomic data. The platform is compatible with multiple Hi-C data versions and boasts a highly customizable interface, including a configuration panel for the precise adjustment of key visualization parameters. The tool's interactive features offer a broad range of views, from whole-genome landscapes to detailed interactions between pairs of loci, that are accessible within a single, integrated environment. Here, we demonstrate how using ppHiC to visualize an altered chromatin conformational landscape in neuroblastoma can inform understanding of the genomic rearrangements in this cancer.

DeCGR: an interactive toolkit for deciphering complex genomic rearrangements from Hi-C data

BACKGROUND

Complex genomic rearrangements (CGRs) drive the restructuring of chromatin architecture, resulting in significant interactions among rearranged fragments, visible as anomalous interaction blocks in chromatin contact maps generated by chromosome conformation capture technologies such as Hi-C. These blocks not only offer the orientation and genome coordinates of rearranged fragments but also filter out false positive CGRs, thereby facilitating CGR assembly. Despite this, there is a lack of interactive graphical software tailored for this purpose.

RESULTS

We present DeCGR, a user-friendly Python toolbox specifically designed for deciphering CGRs in Hi-C data. DeCGR consists of four independent execution components. The Breakpoint Filtering module identifies and filters simple rearrangements, providing the coordinates of rearrangement breakpoints. The Fragment Assembly module automatically assembles CGRs and visualizes the assembly process, facilitating the direct association between anomalous interaction blocks and CGR events. The Validation CGRs module verifies the completeness and accuracy of CGRs by generating the Hi-C map with CGRs through a simulation process and examines the difference from the original Hi-C maps. This module displays both the original and the simulated Hi-C map with highlighted rearranged fragment boundaries for rapid review to assess the CGRs. Finally, the Reconstruct Hi-C Map module provides the reconstructed Hi-C map based on the determined CGRs, allowing users to directly observe the impact of rearrangements on chromatin structure.

CONCLUSIONS

DeCGR is designed specifically for biologists who aim to explore CGRs from Hi-C data. It provides a validation module to ensure the completeness and correctness of CGRs. Additionally, it allows users to generate CGR assembly results and reconstruct the Hi-C map with just one click. DeCGR provides intuitive visualization results for each module, allowing users to easily associate CGRs with Hi-C maps. DeCGR is operable through a user-friendly graphical interface. Source codes are freely available at https://github.com/GaoLabXDU/DeCGR .

PWOs repress gene transcription by regulating chromatin structures in Arabidopsis

PWWP-DOMAIN INTERACTOR OF POLYCOMBS (PWO) family proteins play a vital role in regulating plant development. However, the molecular mechanisms of how PWOs regulate chromatin structure is elusive. Our data show that the PWO1 binding sites are enriched with positive modifications but exclusive with H3K27me3. Moreover, PWO1 binds to the H3K27me3-enriched compartment domain (H3K27me3-CD) boundary regions, and functions to maintain the boundary strength. Meanwhile, we found that PWOs and Polycomb repressive complex 2 (PRC2) function parallelly in maintaining H3K27me3-CDs' structure. Loss of either PWOs or PRC2 leads to H3K27me3-CD strength reduction, B to A compartment switching as well as the H3K27me3-CD relocating away from the nuclear periphery. Additionally, PWOs and lamin-like proteins collaborate to regulate multiple chromatin structures to repress gene transcription within H3K27me3-CDs. We conclude that PWOs maintain H3K27me3-CDs' repressive state and regulate their spatial position in the nucleus.

Genome assembly of an endemic butterfly (Minois Aurata) shed light on the genetic mechanisms underlying ecological adaptation to arid valley habitat

BACKGROUND

The Hengduan Mountains, one of the global biodiversity hotspots with exceptional species richness and high endemism, contains numerous arid valleys that create a distinctive geographical and ecological landscape. However, the adaptive evolutionary mechanisms of organism in the arid valley remain poorly understood. Minois aurata, an endemic butterfly species found exclusively in the arid valley of the upper Minjiang River, represents an attractive model system for studying adaptive evolutionary mechanisms to arid valley environments.

RESULTS

Here, we present the first chromosome-level genome assembly for Minois aurata, with a total size of approximately 609.17 Mb, and a scaffold N50 size of 23.88 Mb. These scaffolds were further clustered and anchored onto 29 chromosomes based on Hi-C data. A total of 16,163 protein-coding genes were predicted, of which 91.83% were functionally annotated. The expansion of transposable elements (TEs) accounts for the relatively large genome size of M. aurata, potentially aiding its adaptation to environmental conditions. Phylogenomic analyses based on 3,785 single-copy genes revealed that M. aurata is most closely related to Hipparchia semele. Further mitochondrial genome analysis of four Minois species placed M. aurata in a basal position within the genus, supporting it as an independent species. A total of 185 rapidly evolving and 232 specific gene families were identified in M. aurata. Functional enrichment analysis indicated that these gene families were mainly associated with ultraviolet radiation, heat and hypoxia responses. We also identified 234 positive selected genes in M. aurata, some of which are related to compound eye photoreceptor development, osmotic stress, and light stimulus response. Demographic analysis indicated that the effective population size of M. aurata decreased around 0.4 and 0.04 million years ago, respectively, coinciding with the localized sub-glaciation.

CONCLUSION

The chromosome-level genome offers a comprehensive genomic basis for understanding the evolutionary and adaptive strategies of Minois aurata in the unique arid valley environment of the Hengduan Mountains, while also providing valuable insights into the broader mechanisms of organism adaptation to such habitats.

Elevated EGR1 Binding at Enhancers in Excitatory Neurons Correlates with Neuronal Subtype-Specific Epigenetic Regulation

Brain development and neuronal cell specification are accompanied with epigenetic changes to achieve diverse gene expression regulation. Interacting with cell-type specific epigenetic marks, transcription factors bind to different sets of cis-regulatory elements in different types of cells. Currently, it remains largely unclear how cell-type specific gene regulation is achieved for neurons. In this study, we generated epigenetic maps to perform comparative histone modification analysis between excitatory and inhibitory neurons. We found that neuronal cell-type specific histone modifications are enriched in super enhancer regions containing abundant EGR1 motifs. Further CUT&RUN data validated that more EGR1 binding sites can be detected in excitatory neurons and primarily located in enhancers. Integrative analysis revealed that EGR1 binding is strongly correlated with various epigenetic markers for open chromatin regions and associated with distinct gene pathways with neuronal subtype-specific functions. In inhibitory neurons, the majority of genomic regions hosting EGR1 binding sites become accessible at early embryonic stages. In contrast, the super enhancers in excitatory neurons hosting EGR1 binding sites gained their accessibility during postnatal stages. This study highlights the significance of transcription factor binding to enhancer regions, which may play a crucial role in establishing cell-type specific gene regulation in neurons.

Disorganized chromatin hierarchy and stem cell aging in a male patient of atypical laminopathy-based progeria mandibuloacral dysplasia type A

Studies of laminopathy-based progeria offer insights into aging-associated diseases and highlight the role of LMNA in chromatin organization. Mandibuloacral dysplasia type A (MAD) is a largely unexplored form of atypical progeria that lacks lamin A post-translational processing defects. Using iPSCs derived from a male MAD patient carrying homozygous LMNA p.R527C, premature aging phenotypes are recapitulated in multiple mesenchymal lineages, including mesenchymal stem cells (MSCs). Comparison with 26 human aging MSC expression datasets reveals that MAD-MSCs exhibit the highest similarity to senescent primary human MSCs. Lamina-chromatin interaction analysis reveals reorganization of lamina-associating domains (LADs) and repositioning of non-LAD binding peaks may contribute to the observed accelerated senescence. Additionally, 3D genome organization further supports hierarchical chromatin disorganization in MAD stem cells, alongside dysregulation of genes involved in epigenetic modification, stem cell fate maintenance, senescence, and geroprotection. Together, these findings suggest LMNA missense mutation is linked to chromatin alterations in an atypical progeroid syndrome.

Multiscale 3D genome rewiring during PTF1A-mediated somatic cell reprogramming into neural stem cells

The genome is intricately folded into chromatin compartments, topologically associating domains (TADs) and loops unique to each cell type. How this higher-order genome organization regulates cell fate transition remains elusive. Here we show how a single non-neural progenitor transcription factor, PTF1A, reorchestrates the 3D genome during fibroblast transdifferentiation into neural stem cells (NSCs). Multiomics analyses integrating Hi-C data, PTF1A and CTCF DNA-binding profiles, H3K27ac modification, and gene expression, demonstrate that PTF1A binds to subTAD boundaries subsequently associated with elevated CTCF binding and enhanced boundary insulation, and reorganizes chromatin loops, leading to gene expression changes that drive transdifferentiation into NSCs. Moreover, PTF1A activates enhancers and super-enhancers near low-insulation boundaries and modulates H3K27ac deposition, promoting cell fate transitions. Together, our data implicate an involvement of 3D genome in transcriptional and cell fate alterations, and highlight an essential role for PTF1A in gene expression control and multiscale 3D genome remodeling during cell reprogramming.

The chromosome-level genome assembly and annotation of an invasive forest pest Obolodiplosis robiniae

Biological invasion is a major global problem, leading to the loss of biodiversity and species extinction, and causing huge economic losses to countries. Obolodiplosis robiniae is a major invasive forest pest that has caused economic losses in Asia and Europe. Here, the chromosome- level genome of O. robiniae was assembled using the PacBio platform and Hi-C technology. A contig-level genome with a length of 199.49 Mb and a contig N50 of 4.66 Mb was assembled. Approximately 98.05% of contigs were successfully anchored to four chromosomes using Hi-C assisted genome assembly. The genome integrity was assessed to be 90.3% based on BUSCOs analysis. The high-quality genome provides valuable data for the study of invasive species, and a foundation for the understanding the biology and ecology of O. robiniae.

ChromaFold predicts the 3D contact map from single-cell chromatin accessibility

Identifying cell-type-specific 3D chromatin interactions between regulatory elements can help decipher gene regulation and interpret disease-associated non-coding variants. However, achieving this resolution with current 3D genomics technologies is often infeasible given limited input cell numbers. We therefore present ChromaFold, a deep learning model that predicts 3D contact maps, including regulatory interactions, from single-cell ATAC sequencing (scATAC-seq) data alone. ChromaFold uses pseudobulk chromatin accessibility, co-accessibility across metacells, and a CTCF motif track as inputs and employs a lightweight architecture to train on standard GPUs. Trained on paired scATAC-seq and Hi-C data in human samples, ChromaFold accurately predicts the 3D contact map and peak-level interactions across diverse human and mouse test cell types. Compared to leading contact map prediction models that use ATAC-seq and CTCF ChIP-seq, ChromaFold achieves state-of-the-art performance using only scATAC-seq. Finally, fine-tuning ChromaFold on paired scATAC-seq and Hi-C in a complex tissue enables deconvolution of chromatin interactions across cell subpopulations.

Convergent Degenerated Regulatory Elements Associated with Limb Loss in Limbless Amphibians and Reptiles

Limbs are a defining characteristic of tetrapods, yet numerous taxa, primarily among amphibians and reptiles, have independently lost limbs as an adaptation to new ecological niches. To elucidate the genetic factors contributing to this convergent limb loss, we present a 12 Gb chromosome-level assembly of the Banna caecilian (Ichthyophis bannanicus), a limbless amphibian. Our comparative analysis, which includes the reconstruction of amphibian karyotype evolution, reveals constrained gene length evolution in a subset of developmental genes across 3 large genomes. Investigation of limb development genes uncovered the loss of Grem1 in caecilians and Tulp3 in snakes. Interestingly, caecilians and snakes share a significantly larger number of convergent degenerated conserved noncoding elements than limbless lizards, which have a shorter evolutionary history of limb loss. These convergent degenerated conserved noncoding elements overlap significantly with active genomic regions during mouse limb development and are conserved in limbed species, suggesting their essential role in limb patterning in the tetrapod common ancestor. While most convergent degenerated conserved noncoding elements emerged in the jawed vertebrate ancestor, coinciding with the origin of paired appendage, more recent degenerated conserved noncoding elements also contribute to limb development, as demonstrated through functional experiments. Our study provides novel insights into the regulatory elements associated with limb development and loss, offering an evolutionary perspective on the genetic basis of morphological specialization.

Development and evolution of Drosophila chromatin landscape in a 3D genome context

Little is known about how the epigenomic states change during development and evolution in a 3D genome context. Here we use Drosophila pseudoobscura with complex turnover of sex chromosomes as a model to address this, by collecting massive epigenomic and Hi-C data from five developmental stages and three adult tissues. We reveal that over 60% of the genes and transposable elements (TE) exhibit at least one developmental transition of chromatin state. Transitions on specific but not housekeeping enhancers are associated with specific chromatin loops and topologically associated domain borders (TABs). While evolutionarily young TEs are generally silenced, old TEs more often have been domesticated as interacting TABs or specific enhancers. But on the recently evolved X chromosome, young TEs are instead often active and recruited as TABs, due to acquisition of dosage compensation. Overall we characterize how Drosophila epigenomic landscapes change during development and in response to chromosome evolution, and highlight the important roles of TEs in genome organization and regulation.

Chromosome-level genome assembly of Scathophaga stercoraria provides new insights into the evolutionary adaptations of dung flies

The yellow dung fly Scathophaga stercoraria is a widely distributed species in high-altitude regions of the Northern Hemisphere. It plays important roles as a decomposer, predator, and pollinator in the ecosystem. As a staple model organism, S. stercoraria serves as a standard test species for assessing the toxicity of drug residues in livestock dung and has been the focus of numerous studies. The genetic mechanisms underlying the ecological adaptability of S. stercoraria remain poorly understood. To fill the gap, we first assembled a high-quality chromosome-level genome of S. stercoraria, resulting in a final assembly size of 549.64 Mb, with a contig N50 of 4.06 Mb, and 92.53 % of the sequence anchored to six chromosomes. Gene family analysis revealed an expansion of Toll (Toll1), GNBP3, Cyp303a1, Cyp4d14, Cyp6g1, OR67d, and yolk protein genes in the S. stercoraria genome. Transcriptome analysis indicated that most genes in the trypsin and carboxypeptidase gene families are predominantly expressed during the larval stage, whereas the α-Amylase gene family is mainly expressed during the adult stage. Additionally, PGRP-SC is highly expressed during the larval stage, OBPs are primarily expressed during the adult stage, and yolk protein genes exhibit female-biased expression. Our study not only provides a new resource for the dung flies genomic pool, but also identifies the expression patterns of key ecologically adaptative genes and gene families at the developmental stages, which provides new insights into the ecological adaptive evolution of dung flies.

De novo genome assemblies of two cryptodiran turtles with ZZ/ZW and XX/XY sex chromosomes provide insights into patterns of genome reshuffling and uncover novel 3D genome folding in amniotes

Understanding the evolution of chromatin conformation among species is fundamental to elucidate the architecture and plasticity of genomes. Nonrandom interactions of linearly distant loci regulate gene function in species-specific patterns, affecting genome function, evolution, and, ultimately, speciation. Yet, data from nonmodel organisms are scarce. To capture the macroevolutionary diversity of vertebrate chromatin conformation, here we generate de novo genome assemblies for two cryptodiran (hidden-neck) turtles via Illumina sequencing, chromosome conformation capture, and RNA-seq: Apalone spinifera (ZZ/ZW, 2n = 66) and Staurotypus triporcatus (XX/XY, 2n = 54). We detected differences in the three-dimensional (3D) chromatin structure in turtles compared to other amniotes beyond the fusion/fission events detected in the linear genomes. Namely, whole-genome comparisons revealed distinct trends of chromosome rearrangements in turtles: (1) a low rate of genome reshuffling in Apalone (Trionychidae) whose karyotype is highly conserved when compared to chicken (likely ancestral for turtles), and (2) a moderate rate of fusions/fissions in Staurotypus (Kinosternidae) and Trachemys scripta (Emydidae). Furthermore, we identified a chromosome folding pattern that enables "centromere-telomere interactions" previously undetected in turtles. The combined turtle pattern of "centromere-telomere interactions" (discovered here) plus "centromere clustering" (previously reported in sauropsids) is novel for amniotes and it counters previous hypotheses about amniote 3D chromatin structure. We hypothesize that the divergent pattern found in turtles originated from an amniote ancestral state defined by a nuclear configuration with extensive associations among microchromosomes that were preserved upon the reshuffling of the linear genome.

Genomic insights into adaptive evolution of the species-rich cosmopolitan plant genus Rhododendron

The species-rich cosmopolitan genus Rhododendron offers a good system for exploring the genomic mechanisms underlying adaptation to diverse habitats. Here, we report high-quality chromosomal-level genome assemblies of nine species, representing all five subgenera, different altitudinal distributions, and all flower color types of this genus. Further comprehensive genomic analyses indicate diverse adaptive strategies employed by Rhododendron, particularly adaptation to alpine and subalpine habitats by expansion/contraction of gene families involved in pathogen defense and oxidative phosphorylation, genomic convergent evolution, and gene copy-number variation. The convergent adaptation to high altitudes is further shown by population genomic analysis of R. nivale from the Himalaya-Hengduan Mountains. Moreover, we identify the genes involved in the biosynthesis of anthocyanins and carotenoids, which play a crucial role in shaping flower color diversity and environmental adaptation. Our study is significant for comprehending plant adaptive evolution and the uneven distribution of species diversity across different geographical regions.

Effects of Differentially Methylated CpG Sites in Enhancer and Promoter Regions on the Chromatin Structures of Target LncRNAs in Breast Cancer

Aberrant DNA methylation plays a crucial role in breast cancer progression by regulating gene expression. However, the regulatory pattern of DNA methylation in long noncoding RNAs (lncRNAs) for breast cancer remains unclear. In this study, we integrated gene expression, DNA methylation, and clinical data from breast cancer patients included in The Cancer Genome Atlas (TCGA) database. We examined DNA methylation distribution across various lncRNA categories, revealing distinct methylation characteristics. Through genome-wide correlation analysis, we identified the CpG sites located in lncRNAs and the distally associated CpG sites of lncRNAs. Functional genome enrichment analysis, conducted through the integration of ENCODE ChIP-seq data, revealed that differentially methylated CpG sites (DMCs) in lncRNAs were mostly located in promoter regions, while distally associated DMCs primarily acted on enhancer regions. By integrating Hi-C data, we found that DMCs in enhancer and promoter regions were closely associated with the changes in three-dimensional chromatin structures by affecting the formation of enhancer-promoter loops. Furthermore, through Cox regression analysis and three machine learning models, we identified 11 key methylation-driven lncRNAs (DIO3OS, ELOVL2-AS1, MIAT, LINC00536, C9orf163, AC105398.1, LINC02178, MILIP, HID1-AS1, KCNH1-IT1, and TMEM220-AS1) that were associated with the survival of breast cancer patients and constructed a prognostic risk scoring model, which demonstrated strong prognostic performance. These findings enhance our understanding of DNA methylation's role in lncRNA regulation in breast cancer and provide potential biomarkers for diagnosis.

The impact of the embryonic DNA methylation program on CTCF-mediated genome regulation

During mammalian embryogenesis, both the 5-cytosine DNA methylation (5meC) landscape and three dimensional (3D) chromatin architecture are profoundly remodeled during a process known as 'epigenetic reprogramming.' An understudied aspect of epigenetic reprogramming is how the 5meC flux, per se, affects the 3D genome. This is pertinent given the 5meC-sensitivity of DNA binding for a key regulator of chromosome folding: CTCF. We profiled the CTCF binding landscape using a mouse embryonic stem cell (ESC) differentiation protocol that models embryonic 5meC dynamics. Mouse ESCs lacking DNA methylation machinery are able to exit naive pluripotency, thus allowing for dissection of subtle effects of CTCF on gene expression. We performed CTCF HiChIP in both wild-type and mutant conditions to assess gained CTCF-CTCF contacts in the absence of 5meC. We performed H3K27ac HiChIP to determine the impact that ectopic CTCF binding has on cis-regulatory contacts. Using 5meC epigenome editing, we demonstrated that the methyl-mark is able to impair CTCF binding at select loci. Finally, a detailed dissection of the imprinted Zdbf2 locus showed how 5meC-antagonism of CTCF allows for proper gene regulation during differentiation. This work provides a comprehensive overview of how 5meC impacts the 3D genome in a relevant model for early embryonic events.

Drought-responsive dynamics of H3K9ac-marked 3D chromatin interactions are integrated by OsbZIP23-associated super-enhancer-like promoter regions in rice

BACKGROUND

In response to drought stress (DS), plants undergo complex processes that entail significant transcriptome reprogramming. However, the intricate relationship between the dynamic alterations in the three-dimensional (3D) genome and the modulation of gene co-expression in drought responses remains a relatively unexplored area.

RESULTS

In this study, we reconstruct high-resolution 3D genome maps based on genomic regions marked by H3K9ac, an active histone modification that dynamically responds to soil water variations in rice. We discover a genome-wide disconnection of 3D genome contact upon DS with over 10,000 chromatin loops lost, which are partially recovered in the subsequent re-watering. Loops integrating promoter-promoter interactions (PPI) contribute to gene expression in addition to basal H3K9ac modifications. Moreover, H3K9ac-marked promoter regions with high affinities in mediating PPIs, termed as super-promoter regions (SPRs), integrate spatially clustered PPIs in a super-enhancer-like manner. Interestingly, the knockout mutation of OsbZIP23, a well-defined DS-responsive transcription factor, leads to the disassociation of over 80% DS-specific PPIs and decreased expression of the corresponding genes under DS. As a case study, we show how OsbZIP23 integrates the PPI cluster formation and the co-expression of four dehydrin genes, RAB16A-D, through targeting the RAB16C SPR in a stress signaling-dependent manner.

CONCLUSIONS

Our high-resolution 3D genome maps unveil the principles and details of dynamic genome folding in response to water supply variations and illustrate OsbZIP23 as an indispensable integrator of the yet unique 3D genome organization that is essential for gene co-expression under DS in rice.

T2T genome assemblies of Fallopia multiflora (Heshouwu) and F. multiflora var. angulata

The traditional Chinese medicinal plant Fallopia multiflora (hereafter AYY) is well known for its anti-hyperlipidaemia, immunomodulating, and hepatoprotective effects, attributed to its abundance of anthraquinones and stilbene glycosides, which are distinct to its variety F. multiflora var. angulata (hereafter CYY) in proportion and composition. In this study, telomere-to-telomere (T2T) genomes were assembled for AYY and CYY using PacBio HiFi reads and Hi-C data. The genome sizes, percentages of repetitive sequences, and numbers of protein-coding genes of AYY and CYY assemblies were 1,458.37 Mb/70.48%/84,768 and 1,174.38 Mb/67.36%/69,100, respectively. Comprehensive assessments confirmed high continuity (contig N50: 112.58 Mb and 94.83 Mb; number of gaps: 9 and 5), completeness (BUSCOs: 97.30% and 97.60%; LAI: 16.93 and 16.77), and correctness (QV: 51.42 and 52.60) of AYY and CYY assemblies. These T2T genomes of F. multiflora provide valuable resources for studying the biosynthesis of specialized metabolites and facilitating precise genetic improvement.

Congenital microcoria deletion in mouse links Sox21 dysregulation to disease and suggests a role for TGFB2 in glaucoma and myopia

Congenital microcoria (MCOR) is a rare hereditary developmental defect of the iris dilator muscle frequently associated with high axial myopia and high intraocular pressure (IOP) glaucoma. The condition is caused by submicroscopic rearrangements of chromosome 13q32.1. However, the mechanisms underlying the failure of iris development and the origin of associated features remain elusive. Here, we present a 3D architecture model of the 13q32.1 region, demonstrating that MCOR-related deletions consistently disrupt the boundary between two topologically associating domains (TADs). Deleting the critical MCOR-causing region in mice reveals ectopic Sox21 expression precisely aligning with Dct, each located in one of the two neighbor TADs. This observation is consistent with the TADs' boundary alteration and adoption of Dct regulatory elements by the Sox21 promoter. Additionally, we identify Tgfb2 as a target gene of SOX21 and show TGFΒ2 accumulation in the aqueous humor of an MCOR-affected subject. Accumulation of TGFB2 is recognized for its role in glaucoma and potential impact on axial myopia. Our results highlight the importance of SOX21-TGFB2 signaling in iris development and control of eye growth and IOP. Insights from MCOR studies may provide therapeutic avenues for this condition but also for glaucoma and high myopia conditions, affecting millions of people.

The formation and propagation of human Robertsonian chromosomes

Robertsonian chromosomes are a type of variant chromosome found commonly in nature. Present in one in 800 humans, these chromosomes can underlie infertility, trisomies, and increased cancer incidence. Recognized cytogenetically for more than a century, their origins have remained mysterious. Recent advances in genomics allowed us to assemble three human Robertsonian chromosomes completely. We identify a common breakpoint and epigenetic changes in centromeres that provide insight into the formation and propagation of common Robertsonian translocations. Further investigation of the assembled genomes of chimpanzee and bonobo highlights the structural features of the human genome that uniquely enable the specific crossover event that creates these chromosomes. Resolving the structure and epigenetic features of human Robertsonian chromosomes at a molecular level paves the way to understanding how chromosomal structural variation occurs more generally, and how chromosomes evolve.

HiCMC: High-Efficiency Contact Matrix Compressor

BACKGROUND

Chromosome organization plays an important role in biological processes such as replication, regulation, and transcription. One way to study the relationship between chromosome structure and its biological functions is through Hi-C studies, a genome-wide method for capturing chromosome conformation. Such studies generate vast amounts of data. The problem is exacerbated by the fact that chromosome organization is dynamic, requiring snapshots at different points in time, further increasing the amount of data to be stored. We present a novel approach called the High-Efficiency Contact Matrix Compressor (HiCMC) for efficient compression of Hi-C data.

RESULTS

By modeling the underlying structures found in the contact matrix, such as compartments and domains, HiCMC outperforms the state-of-the-art method CMC by approximately 8% and the other state-of-the-art methods cooler, LZMA, and bzip2 by over 50% across multiple cell lines and contact matrix resolutions. In addition, HiCMC integrates domain-specific information into the compressed bitstreams that it generates, and this information can be used to speed up downstream analyses.

CONCLUSION

HiCMC is a novel compression approach that utilizes intrinsic properties of contact matrix, such as compartments and domains. It allows for a better compression in comparison to the state-of-the-art methods. HiCMC is available at https://github.com/sXperfect/hicmc .

A near-complete chromosome-level genome assembly of looseleaf lettuce (Lactuca sativa var. crispa)

Lettuce (Lactuca sativa L., Asteraceae) is one of the most important vegetable crops, known for its various horticultural types and significant morphological variation. The first reference genome of lettuce, a crisphead type (L. sativa var. capitata cv. Salinas), was previously released. Here, we reported a near-complete chromosome-level reference genome for looseleaf lettuce (L. sativa var. crispa). PacBio high-fidelity sequencing, Oxford Nanopore, and Hi-C technologies were employed to produce genome assembly. The final assembly is 2.59 Gb in length with a contig N50 of 205.47 Mb, anchored onto nine chromosomes, containing 14 recognizable telomeres and only 11 gaps. Repetitive sequences account for 77.11% of the genome, and 41,375 protein-coding genes were predicted, with 99.10% of these assigned functional annotations. This chromosome-level genome enriched genomic resources for various horticultural types of lettuce and will facilitate the characterization of morphological variation and genetic improvement in lettuce.

The gap-free genome of Forsythia suspensa illuminates the intricate landscape of centromeres

Forsythia suspensa, commonly known as weeping forsythia, holds significance in traditional medicine and horticulture. Despite its ecological and cultural importance, the existing reference genome presents challenges with duplications and gaps, hindering in-depth genomic analyses. Here, we present a Telomere-to-Telomere (T2T) assembly of the F. suspensa genome, integrating Oxford Nanopore Technologies (ONT) ultra-long, Hi-C datasets, and high-fidelity (HiFi) sequencing data. The T2T reference genome (Fsus-CHAU) consists of 14 chromosomes, totaling 688.79 Mb, and encompasses 33 932 predicted protein-coding genes. Additionally, we characterize functional centromeres in the F. suspensa genome by developing a specific CENH3 antibody. We demonstrate that centromeric regions in F. suspensa exhibit a diverse array of satellites, showcasing distinctive types with unconventional lengths across various chromosomes. This discovery offers implications for the adaptability of CENH3 and the potential influence on centromere dynamics. Furthermore, after assessing the insertion time of full-length LTRs within centromeric regions, we found that they are older compared to those across the entire genome, contrasting with observations in other species where centromeric retrotransposons are typically young. We hypothesize that asexual reproduction may impact retrotransposon dynamics, influencing centromere evolution. In conclusion, our T2T assembly of the F. suspensa genome, accompanied by detailed genomic annotations and centromere analysis, significantly enhances F. suspensa potential as a subject of study in fields ranging from ecology and horticulture to traditional medicine.

ENT3C: an entropy-based similarity measure for Hi-C and micro-C derived contact matrices

Hi-C and micro-C sequencing have shed light on the profound importance of 3D genome organization in cellular function by probing 3D contact frequencies across the linear genome. The resulting contact matrices are extremely sparse and susceptible to technical- and sequence-based biases, making their comparison challenging. The development of reliable, robust and efficient methods for quantifying similarity between contact matrices is crucial for investigating variations in the 3D genome organization in different cell types or under different conditions, as well as evaluating experimental reproducibility. We present a novel method, ENT3C, which measures the change in pattern complexity in the vicinity of contact matrix diagonals to quantify their similarity. ENT3C provides a robust, user-friendly Hi-C or micro-C contact matrix similarity metric and a characteristic entropy signal that can be used to gain detailed biological insights into 3D genome organization.

Loss of multi-level 3D genome organization during breast cancer progression

Breast cancer entails intricate alterations in genome organization and expression. However, how three-dimensional (3D) chromatin structure changes in the progression from a normal to a breast cancer malignant state remains unknown. To address this, we conducted an analysis combining Hi-C data with lamina-associated domains (LADs), epigenomic marks, and gene expression in an in vitro model of breast cancer progression. Our results reveal that while the fundamental properties of topologically associating domains (TADs) are overall maintained, significant changes occur in the organization of compartments and subcompartments. These changes are closely correlated with alterations in the expression of oncogenic genes. We also observe a restructuring of TAD-TAD interactions, coinciding with a loss of spatial compartmentalization and radial positioning of the 3D genome. Notably, we identify a previously unrecognized interchromosomal insertion event, wherein a locus on chromosome 8 housing the MYC oncogene is inserted into a highly active subcompartment on chromosome 10. This insertion is accompanied by the formation of de novo enhancer contacts and activation of MYC, illustrating how structural genomic variants can alter the 3D genome to drive oncogenic states. In summary, our findings provide evidence for the loss of genome organization at multiple scales during breast cancer progression revealing novel relationships between genome 3D structure and oncogenic processes.

Evolutionary patterns and functional effects of 3D chromatin structures in butterflies with extensive genome rearrangements

Chromosome rearrangements may distort 3D chromatin architectures and thus change gene regulation, yet how 3D chromatin structures evolve in insects is largely unknown. Here, we obtain chromosome-level genomes for four butterfly species, Graphium cloanthus, Graphium sarpedon, Graphium eurypylus with 2n = 30, 40, and 60, respectively, and Papilio bianor with 2n = 60. Together with large-scale Hi-C data, we find that inter-chromosome rearrangements very rarely disrupted the pre-existing 3D chromatin structure of ancestral chromosomes. However, some intra-chromosome rearrangements changed 3D chromatin structures compared to the ancestral configuration. We find that new TADs and subTADs have emerged across the rearrangement sites where their adjacent compartments exhibit uniform types. Two intra-chromosome rearrangements altered Rel and lft regulation, potentially contributing to wing patterning differentiation and host plant choice. Notably, butterflies exhibited chromatin loops between Hox gene cluster ANT-C and BX-C, unlike Drosophila. Our CRISPR-Cas9 experiments in butterflies confirm that knocking out the CTCF binding site of the loops in BX-C affected the phenotypes regulated by Antp in ANT-C, resulting in legless larva. Our results reveal evolutionary patterns of insect 3D chromatin structures and provide evidence that 3D chromatin structure changes can play important roles in the evolution of traits.

DiffGR: Detecting Differentially Interacting Genomic Regions from Hi-C Contact Maps

Recent advances in high-throughput chromosome conformation capture (Hi-C) techniques have allowed us to map genome-wide chromatin interactions and uncover higher-order chromatin structures, thereby shedding light on the principles of genome architecture and functions. However, statistical methods for detecting changes in large-scale chromatin organization such as topologically associating domains (TADs) are still lacking. Here, we proposed a new statistical method, DiffGR, for detecting differentially interacting genomic regions at the TAD level between Hi-C contact maps. We utilized the stratum-adjusted correlation coefficient to measure similarity of local TAD regions. We then developed a nonparametric approach to identify statistically significant changes of genomic interacting regions. Through simulation studies, we demonstrated that DiffGR can robustly and effectively discover differential genomic regions under various conditions. Furthermore, we successfully revealed cell type-specific changes in genomic interacting regions in both human and mouse Hi-C datasets, and illustrated that DiffGR yielded consistent and advantageous results compared with state-of-the-art differential TAD detection methods. The DiffGR R package is published under the GNU General Public License (GPL) ≥ 2 license and is publicly available at https://github.com/wmalab/DiffGR.

DBD-α4 helix of EWSR1::FLI1 is required for GGAA microsatellite binding that underlies genome regulation in Ewing sarcoma

Ewing sarcoma is the second most common bone cancer in children and young adults. In 85% of patients, a translocation between chromosomes 11 and 22 results in a potent fusion oncoprotein, EWSR1::FLI1. EWSR1::FLI1 is the only genetic alteration in an otherwise unaltered genome of Ewing sarcoma tumors. The EWSR1 portion of the protein is an intrinsically disordered domain involved in transcriptional regulation by EWSR1::FLI1. The FLI portion of the fusion contains a DNA binding domain shown to bind core GGAA motifs and GGAA repeats. A small alpha-helix in the DNA binding domain of FLI1, DBD-𝛼4 helix, is critical for the transcription function of EWSR1::FLI1. In this study, we aimed to understand the mechanism by which the DBD-𝛼4 helix promotes transcription, and therefore oncogenic transformation. We utilized a multi-omics approach to assess chromatin organization, active chromatinmarks, genome binding, and gene expression in cells expressing EWSR1::FLI1 constructs with and without the DBD-𝛼4 helix. Our studies revealed DBD-𝛼4 helix is crucial for cooperative binding of EWSR1::FLI1 at GGAA microsatellites. This binding underlies many aspects of genome regulation by EWSR1::FLI1 such as formation of TADs, chromatin loops, enhancers and productive transcription hubs.

Pre-hypertrophic chondrogenic enhancer landscape of limb and axial skeleton development

Chondrocyte differentiation controls skeleton development and stature. Here we provide a comprehensive map of chondrocyte-specific enhancers and show that they provide a mechanistic framework through which non-coding genetic variants can influence skeletal development and human stature. Working with fetal chondrocytes isolated from mice bearing a Col2a1 fluorescent regulatory sensor, we identify 780 genes and 2'704 putative enhancers specifically active in chondrocytes using a combination of RNA-seq, ATAC-seq and H3K27ac ChIP-seq. Most of these enhancers (74%) show pan-chondrogenic activity, with smaller populations being restricted to limb (18%) or trunk (8%) chondrocytes only. Notably, genetic variations overlapping these enhancers better explain height differences than those overlapping non-chondrogenic enhancers. Finally, targeted deletions of identified enhancers at the Fgfr3, Col2a1, Hhip and, Nkx3-2 loci confirm their role in regulating cognate genes. This enhancer map provides a framework for understanding how genes and non-coding variations influence bone development and diseases.

Chromosome-level genome assembly of ridgetail white shrimp Exopalaemon carinicauda

Exopalaemon carinicauda, a eurythermal and euryhaline shrimp, contributes one third of the total biomass production of polyculture ponds in eastern China and is considered as a potential ideal experimental animal for research on crustaceans. We conducted a high-quality chromosome-level genome assembly of E. carinicauda combining PacBio HiFi and Hi-C sequencing data. The total assembly size was 5.86 Gb, with a contig N50 of 235.52 kb and a scaffold N50 of 138.24 Mb. Approximately 95.29% of the assembled sequences were anchored onto 45 pseudochromosomes. BUSCO analysis revealed that 92.89% of 1,013 single-copy genes were highly conserved orthologs. A total of 44, 288 protein-coding genes were predicted, of which 70.53% were functionally annotated. Given its high heterozygosity (2.62%) and large proportion of repeat sequences (71.49%), it is one of the most complex genome assemblies. This chromosome-scale genome will be a valuable resource for future molecular breeding and functional genomics research on E. carinicauda.

Accelerating 3D genomics data analysis with Microcket

The three-dimensional (3D) organization of genome is fundamental to cell biology. To explore 3D genome, emerging high-throughput approaches have produced billions of sequencing reads, which is challenging and time-consuming to analyze. Here we present Microcket, a package for mapping and extracting interacting pairs from 3D genomics data, including Hi-C, Micro-C, and derivant protocols. Microcket utilizes a unique read-stitch strategy that takes advantage of the long read cycles in modern DNA sequencers; benchmark evaluations reveal that Microcket runs much faster than the current tools along with improved mapping efficiency, and thus shows high potential in accelerating and enhancing the biological investigations into 3D genome. Microcket is freely available at https://github.com/hellosunking/Microcket .

Three-dimensional chromatin reorganization regulates B cell development during ageing

The contribution of three-dimensional genome organization to physiological ageing is not well known. Here we show that large-scale chromatin reorganization distinguishes young and old bone marrow progenitor (pro-) B cells. These changes result in increased interactions at the compartment level and reduced interactions within topologically associated domains (TADs). The gene encoding Ebf1, a key B cell regulator, switches from compartment A to B with age. Genetically reducing Ebf1 recapitulates some features of old pro-B cells. TADs that are most reduced with age contain genes important for B cell development, including the immunoglobulin heavy chain (Igh) locus. Weaker intra-TAD interactions at Igh correlate with altered variable (V), diversity (D) and joining (J) gene recombination. Our observations implicate three-dimensional chromatin reorganization as a major driver of pro-B cell phenotypes that impair B lymphopoiesis with age.

Complete genome assembly provides a high-quality skeleton for pan-NLRome construction in melon

Melon (Cucumis melo L.), being under intensive domestication and selective breeding, displays an abundant phenotypic diversity. Wild germplasm with tolerance to stress represents an untapped genetic resource for discovery of disease-resistance genes. To comprehensively characterize resistance genes in melon, we generate a telomere-to-telomere (T2T) and gap-free genome of wild melon accession PI511890 (C. melo var. chito) with a total length of 375.0 Mb and a contig N50 of 31.24 Mb. The complete genome allows us to dissect genome architecture and identify resistance gene analogs. We construct a pan-NLRome using seven melon genomes, which include 208 variable and 18 core nucleotide-binding leucine-rich repeat receptors (NLRs). Multiple disease-related transcriptome analyses indicate that most up-regulated NLRs induced by pathogens are shell or cloud NLRs. The T2T gap-free assembly and the pan-NLRome not only serve as essential resources for genomic studies and molecular breeding of melon but also provide insights into the genome architecture and NLR diversity.

A chromosome-level genome assembly of Chinese quince (Pseudocydonia sinensis)

Introduction

Pseudocydonia sinensis, also known as Chinese quince, is a perennial shrub or small tree highly valued for its edibility and medicinal properties.

Method

This study presents the first chromosome-level genome assembly of P. sinensis, achieved using HiFi sequencing and Hi-C scaffolding technology.

Results

The assembly resulted in a high-quality genome of 576.39 Mb in size. The genome was anchored to 17 pseudo-chromosomes, with a contig N50 of 27.6 Mb and a scaffold N50 of 33.8 Mb. Comprehensive assessment using BUSCO, CEGMA and BWA tools indicates the high completeness and accuracy of the genome assembly. Our analysis identified 116 species-specific genes, 1196 expanded genes and 1109 contracted genes. Additionally, the distribution of 4DTv values suggests that the most recent duplication event occurred before the divergence of P. sinensis from both Chaenomeles pinnatifida and Pyrus pyrifolia.

Discussion

The assembly of this high-quality genome provides a valuable platform for the genetic breeding and cultivation of P. sinensis, as well as for the comparison of the genetic complexity of P. sinensis with other important crops in the Rosaceae family.

A comprehensive benchmarking with interpretation and operational guidance for the hierarchy of topologically associating domains

Topologically associating domains (TADs), megabase-scale features of chromatin spatial architecture, are organized in a domain-within-domain TAD hierarchy. Within TADs, the inner and smaller subTADs not only manifest cell-to-cell variability, but also precisely regulate transcription and differentiation. Although over 20 TAD callers are able to detect TAD, their usability in biomedicine is confined by a disagreement of outputs and a limit in understanding TAD hierarchy. We compare 13 computational tools across various conditions and develop a metric to evaluate the similarity of TAD hierarchy. Although outputs of TAD hierarchy at each level vary among callers, data resolutions, sequencing depths, and matrices normalization, they are more consistent when they have a higher similarity of larger TADs. We present comprehensive benchmarking of TAD hierarchy callers and operational guidance to researchers of life science researchers. Moreover, by simulating the mixing of different types of cells, we confirm that TAD hierarchy is generated not simply from stacking Hi-C heatmaps of heterogeneous cells. Finally, we propose an air conditioner model to decipher the role of TAD hierarchy in transcription.

The jet-like chromatin structure defines active secondary metabolism in fungi

Eukaryotic genomes are spatially organized within the nucleus in a nonrandom manner. However, fungal genome arrangement and its function in development and adaptation remain largely unexplored. Here, we show that the high-order chromosome structure of Fusarium graminearum is sculpted by both H3K27me3 modification and ancient genome rearrangements. Active secondary metabolic gene clusters form a structure resembling chromatin jets. We demonstrate that these jet-like domains, which can propagate symmetrically for 54 kb, are prevalent in the genome and correlate with active gene transcription and histone acetylation. Deletion of GCN5, which encodes a core and functionally conserved histone acetyltransferase, blocks the formation of the domains. Insertion of an exogenous gene within the jet-like domain significantly augments its transcription. These findings uncover an interesting link between alterations in chromatin structure and the activation of fungal secondary metabolism, which could be a general mechanism for fungi to rapidly respond to environmental cues, and highlight the utility of leveraging three-dimensional genome organization in improving gene transcription in eukaryotes.

Su(Hw) interacts with Combgap to establish long-range chromatin contacts

BACKGROUND

Insulator-binding proteins (IBPs) play a critical role in genome architecture by forming and maintaining contact domains. While the involvement of several IBPs in organising chromatin architecture in Drosophila has been described, the specific contribution of the Suppressor of Hairy wings (Su(Hw)) insulator-binding protein to genome topology remains unclear.

RESULTS

In this study, we provide evidence for the existence of long-range interactions between chromatin bound Su(Hw) and Combgap, which was first characterised as Polycomb response elements binding protein. Loss of Su(Hw) binding to chromatin results in the disappearance of Su(Hw)-Combgap long-range interactions and in a decrease in spatial self-interactions among a subset of Su(Hw)-bound genome sites. Our findings suggest that Su(Hw)-Combgap long-range interactions are associated with active chromatin rather than Polycomb-directed repression. Furthermore, we observe that the majority of transcription start sites that are down-regulated upon loss of Su(Hw) binding to chromatin are located within 2 kb of Combgap peaks and exhibit Su(Hw)-dependent changes in Combgap and transcriptional regulators' binding.

CONCLUSIONS

This study demonstrates that Su(Hw) insulator binding protein can form long-range interactions with Combgap, Polycomb response elements binding protein, and that these interactions are associated with active chromatin factors rather than with Polycomb dependent repression.

A CTCF-binding site in the Mdm1-Il22-Ifng locus shapes cytokine expression profiles and plays a critical role in early Th1 cell fate specification

Cytokine expression during T cell differentiation is a highly regulated process that involves long-range promoter-enhancer and CTCF-CTCF contacts at cytokine loci. Here, we investigated the impact of dynamic chromatin loop formation within the topologically associating domain (TAD) in regulating the expression of interferon gamma (IFN-γ) and interleukin-22 (IL-22); these cytokine loci are closely located in the genome and are associated with complex enhancer landscapes, which are selectively active in type 1 and type 3 lymphocytes. In situ Hi-C analyses revealed inducible TADs that insulated Ifng and Il22 enhancers during Th1 cell differentiation. Targeted deletion of a 17 bp boundary motif of these TADs imbalanced Th1- and Th17-associated immunity, both in vitro and in vivo, upon Toxoplasma gondii infection. In contrast, this boundary element was dispensable for cytokine regulation in natural killer cells. Our findings suggest that precise cytokine regulation relies on lineage- and developmental stage-specific interactions of 3D chromatin architectures and enhancer landscapes.

Chromosome-level genome assembly of Odontothrips loti Haliday (Thysanoptera: Thripidae)

As the predominant pest of alfalfa, Odontothrips loti Haliday causes great damages over the major alfalfa-growing regions of China. The characteristics of strong mobility and fecundity make them develop rapidly in the field and hard to be controlled. There is a shortage of bioinformation and limited genomic resources available of O. loti for us to develop novel pest management strategies. In this study, we constructed a chromosome-level reference genome assembly of O. loti with a genome size of 346.59 Mb and scaffold N50 length of 18.52 Mb, anchored onto 16 chromosomes and contained 20128 genes, of which 93.59% were functionally annotated. The results of 99.20% complete insecta_odb10 genes in BUSCO analysis, 91.11% short reads mapped to the ref-genome, and the consistent tendency among the thrips in the distribution of gene length reflects the quality of genome. Our study provided the first report of genome for the genus Odontothrips, which offers a genomic resource for further investigations on evolution and molecular biology of O. loti, contributing to pest management.

Chromosome-level genome assemblies of Musa ornata and Musa velutina provide insights into pericarp dehiscence and anthocyanin biosynthesis in banana

Musa ornata and Musa velutina are members of the Musaceae family and are indigenous to the South and Southeast Asia. They are very popular in the horticultural market, but the lack of genomic sequencing data and genetic studies has hampered efforts to improve their ornamental value. In this study, we generated the first chromosome-level genome assemblies for both species by utilizing Oxford Nanopore long reads and Hi-C reads. The genomes of M. ornata and M. velutina were assembled into 11 pseudochromosomes with genome sizes of 427.85 Mb and 478.10 Mb, respectively. Repetitive sequences comprised 46.70% and 50.91% of the total genomes for M. ornata and M. velutina, respectively. Differentially expressed gene (DEG) and Gene Ontology (GO) enrichment analyses indicated that upregulated genes in the mature pericarps of M. velutina were mainly associated with the saccharide metabolic processes, particularly at the cell wall and extracellular region. Furthermore, we identified polygalacturonase (PG) genes that exhibited higher expression level in mature pericarps of M. velutina compared to other tissues, potentially being accountable for pericarp dehiscence. This study also identified genes associated with anthocyanin biosynthesis pathway. Taken together, the chromosomal-level genome assemblies of M. ornata and M. velutina provide valuable insights into the mechanism of pericarp dehiscence and anthocyanin biosynthesis in banana, which will significantly contribute to future genetic and molecular breeding efforts.

Cooltools: Enabling high-resolution Hi-C analysis in Python

Chromosome conformation capture (3C) technologies reveal the incredible complexity of genome organization. Maps of increasing size, depth, and resolution are now used to probe genome architecture across cell states, types, and organisms. Larger datasets add challenges at each step of computational analysis, from storage and memory constraints to researchers' time; however, analysis tools that meet these increased resource demands have not kept pace. Furthermore, existing tools offer limited support for customizing analysis for specific use cases or new biology. Here we introduce cooltools (https://github.com/open2c/cooltools), a suite of computational tools that enables flexible, scalable, and reproducible analysis of high-resolution contact frequency data. Cooltools leverages the widely-adopted cooler format which handles storage and access for high-resolution datasets. Cooltools provides a paired command line interface (CLI) and Python application programming interface (API), which respectively facilitate workflows on high-performance computing clusters and in interactive analysis environments. In short, cooltools enables the effective use of the latest and largest genome folding datasets.

Learning Micro-C from Hi-C with diffusion models

In the last few years, Micro-C has shown itself as an improved alternative to Hi-C. It replaced the restriction enzymes in Hi-C assays with micrococcal nuclease (MNase), resulting in capturing nucleosome resolution chromatin interactions. The signal-to-noise improvement of Micro-C allows it to detect more chromatin loops than high-resolution Hi-C. However, compared with massive Hi-C datasets available in the literature, there are only a limited number of Micro-C datasets. To take full advantage of these Hi-C datasets, we present HiC2MicroC, a computational method learning and then predicting Micro-C from Hi-C based on the denoising diffusion probabilistic models (DDPM). We trained our DDPM and other regression models in human foreskin fibroblast (HFFc6) cell line and evaluated these methods in six different cell types at 5-kb and 1-kb resolution. Our evaluations demonstrate that both HiC2MicroC and regression methods can markedly improve Hi-C towards Micro-C, and our DDPM-based HiC2MicroC outperforms regression in various terms. First, HiC2MicroC successfully recovers most of the Micro-C loops even those not detected in Hi-C maps. Second, a majority of the HiC2MicroC-recovered loops anchor CTCF binding sites in a convergent orientation. Third, HiC2MicroC loops share genomic and epigenetic properties with Micro-C loops, including linking promoters and enhancers, and their anchors are enriched for structural proteins (CTCF and cohesin) and histone modifications. Lastly, we find our recovered loops are also consistent with the loops identified from promoter capture Micro-C (PCMicro-C) and Chromatin Interaction Analysis by Paired-End Tag Sequencing (ChIA-PET). Overall, HiC2MicroC is an effective tool for further studying Hi-C data with Micro-C as a template. HiC2MicroC is publicly available at https://github.com/zwang-bioinformatics/HiC2MicroC/.

Tet-mediated DNA methylation dynamics affect chromosome organization

DNA Methylation is a significant epigenetic modification that can modulate chromosome states, but its role in orchestrating chromosome organization has not been well elucidated. Here we systematically assessed the effects of DNA Methylation on chromosome organization with a multi-omics strategy to capture DNA Methylation and high-order chromosome interaction simultaneously on mouse embryonic stem cells with DNA methylation dioxygenase Tet triple knock-out (Tet-TKO). Globally, upon Tet-TKO, we observed weakened compartmentalization, corresponding to decreased methylation differences between CpG island (CGI) rich and poor domains. Tet-TKO could also induce hypermethylation for the CTCF binding peaks in TAD boundaries and chromatin loop anchors. Accordingly, CTCF peak generally weakened upon Tet-TKO, which results in weakened TAD structure and depletion of long-range chromatin loops. Genes that lost enhancer-promoter looping upon Tet-TKO showed DNA hypermethylation in their gene bodies, which may compensate for the disruption of gene expression. We also observed distinct effects of Tet1 and Tet2 on chromatin organization and increased DNA methylation correlation on spatially interacted fragments upon Tet inactivation. Our work showed the broad effects of Tet inactivation and DNA methylation dynamics on chromosome organization.

A fine-scale Arabidopsis chromatin landscape reveals chromatin conformation-associated transcriptional dynamics

Plants, as sessile organisms, deploy transcriptional dynamics for adapting to extreme growth conditions such as cold stress. Emerging evidence suggests that chromatin architecture contributes to transcriptional regulation. However, the relationship between chromatin architectural dynamics and transcriptional reprogramming in response to cold stress remains unclear. Here, we apply a chemical-crosslinking assisted proximity capture (CAP-C) method to elucidate the fine-scale chromatin landscape, revealing chromatin interactions within gene bodies closely associated with RNA polymerase II (Pol II) densities across initiation, pausing, and termination sites. We observe dynamic changes in chromatin interactions alongside Pol II activity alterations during cold stress, suggesting local chromatin dynamics may regulate Pol II activity. Notably, cold stress does not affect large-scale chromatin conformations. We further identify a comprehensive promoter-promoter interaction (PPI) network across the genome, potentially facilitating co-regulation of gene expression in response to cold stress. Our study deepens the understanding of chromatin conformation-associated gene regulation in plant response to cold.

A distal enhancer guides the negative selection of toxic glycoalkaloids during tomato domestication

Steroidal glycoalkaloids (SGAs) are major plant defense metabolites against pests, while they are considered poisonous in food. The genetic basis that guides negative selection of SGAs production during tomato domestication remains poorly understood. Here, we identify a distal enhancer, GAME Enhancer 1 (GE1), as the key regulator of SGAs metabolism in tomato. GE1 recruits MYC2-GAME9 transcriptional complex to regulate the expression of GAME cluster genes via the formation of chromatin loops located in the neighboring DNA region. A naturally occurring GE176 allelic variant is found to be more active in stimulating GAME expression. We show that the weaker GE1 allele has been the main driver for selecting reduced SGAs levels during tomato domestication. Unravelling the "TFs-Enhancer-Promoter" regulatory mechanism operating in SGAs metabolism opens unprecedented prospects for SGAs manipulation in Solanaceae via precision breeding strategies.

EVOLUTIONARY CO-OPTION OF AN ANCESTRAL CLOACAL REGULATORY LANDSCAPE DURING THE EMERGENCE OF DIGITS AND GENITALS

The transition from fins to limbs has been a rich source of discussion for more than a century. One open and important issue is understanding how the mechanisms that pattern digits arose during vertebrate evolution. In this context, the analysis of Hox gene expression and functions to infer evolutionary scenarios has been a productive approach to explain the changes in organ formation, particularly in limbs. In tetrapods, the transcription of Hoxd genes in developing digits depends on a well-characterized set of enhancers forming a large regulatory landscape1,2. This control system has a syntenic counterpart in zebrafish, even though they lack bona fide digits, suggestive of deep homology3 between distal fin and limb developmental mechanisms. We tested the global function of this landscape to assess ancestry and source of limb and fin variation. In contrast to results in mice, we show here that the deletion of the homologous control region in zebrafish has a limited effect on the transcription of hoxd genes during fin development. However, it fully abrogates hoxd expression within the developing cloaca, an ancestral structure related to the mammalian urogenital sinus. We show that similar to the limb, Hoxd gene function in the urogenital sinus of the mouse also depends on enhancers located in this same genomic domain. Thus, we conclude that the current regulation underlying Hoxd gene expression in distal limbs was co-opted in tetrapods from a preexisting cloacal program. The orthologous chromatin domain in fishes may illustrate a rudimentary or partial step in this evolutionary co-option.